1. Field of the Invention
This invention relates generally to transducer suspension systems for magnetic recording media, and more particularly to electrical connections to a transducer head.
2. Description of the Related Art
Direct access storage devices (DASD) such as disk drives store information on concentric tracks of a rotatable magnetic recording disk. A magnetic head or other transducer element is moved from track to track to read or record the desired information. Typically, the magnetic head is positioned on an air-bearing slider which "flies" off of the surface of the disk as the disk rotates. A head suspension assembly connects the slider to a rotary or linear actuator. The head suspension assembly provides support for the slider while allowing it to gimbal during operation in order to adjust its orientation as appropriate.
The head suspension assembly typically comprises a load beam attached to an actuator arm, a flexible member (known as a flexure) attached to the load beam, and a slider attached to the flexure.
Examples of suspension systems are shown in the following references:
U.S. Pat. No. 5,208,712, issued May 4, 1992; U.S. Pat. No. 5,172,286, issued Dec. 15, 1992; U.S. Pat. No. 5,138,507, issued Aug. 11, 1992; U.S. Pat. No. 5,074,029, issued Dec. 24, 1991; U.S. Pat. No. 5,063,464, issued Nov. 5, 1991; U.S. Pat. No. 5,012,368, issued Apr. 30, 1991; U.S. Pat. No. 5,003,420, issued Mar. 26, 1991; U.S. Pat. No. 5,001,583, issued Mar. 19, 1991; U.S. Pat. No. 4,996,623, issued Feb. 26, 1991; U.S. Pat. No. 4,996,616, issued Feb. 26, 1991; U.S. Pat. No. 4,991,045, issued Feb. 5, 1991; U.S. Pat. No. 4,937,693, issued Jun. 26, 1990; U.S. Pat. No. 4,853,811, issued Aug. 1, 1989; U.S. Pat. No. 4,884,154, issued Nov. 28, 1989; U.S. Pat. No. 4,868,694, issued Sep. 19, 1989; U.S. Pat. No. 4,807,054 issued Feb. 21, 1989; U.S. Pat. No. 4,167,765, issued Sep. 11, 1979; U.S. Pat. No. 3,931,641, issued Jan. 6, 1976; European Patent Application 484,906, published May 13, 1992; European Patent Application 442,225, published Aug. 21, 1991; Japanese Patent Application 01-213821, published Aug. 28, 1989; UK Patent Application 2,193,833, published Feb. 17, 1988; IBM Technical Disclosure Bulletin Vol. 33, No. 10B, March 1991, page 392; IBM Technical Disclosure Bulletin Vol. 32, No. 3A, August 1989, page 175; and IBM Technical Disclosure Bulletin Vol. 31, No. 12, May 1989, page 203.
In order to electrically connect the transducer head with a read/write controller for the a disk drive unit, very thin electrical wires are run across the suspension assembly. One conventional type of suspension assembly, such as that disclosed in U.S. Pat. No. 5,012,368 to Bosier et al., includes a fine tube through which the wires pass to the transducer head. Other suspension assemblies, such as disclosed in U.S. Pat. No. 5,001,583 to Matsuzaki, are manufactured with the wires embedded in the load beam.
Some suspension assemblies pass the wires directly over the load beam, without using a tube that disadvantageously increases weight and affects flexing. This type of suspension assembly is disclosed in U.S. Pat. No. 5,074,029 to Brooks, Jr. et al, entitled "Method for Stringing Wire on an Actuator Arm." As disclosed therein, the load beam is attached to a plastic tail (which is eventually discarded) and affixed to a tooling assembly. The wires are positioned across the load beam and tensioned using a tensioning device on the tooling assembly. A series of glue dots are then applied to adhesively connect the wires to the load beam. Particularly, uv-curable glue is deposited in dots at predetermined locations along the tensioned wires, and the glue dots are then exposed to uv light. After the glue has cured, the wires are ultrasonically bonded to the transducer, cut and formed into a loop, thereby causing a tension imbalance at the glue dot closest to the cut. One problem with this gluing technique is that the glue dot closest to the transducer head sometimes pulls away from the load beam due to the tension imbalance, rendering the part unusable. The glue dots are subjected to further stress during subsequent cleaning in an ultrasound bath in which the part is shaken. Additionally, the water in the bath causes the glue to swell, which can also contribute to failure of the glue dot. Furthermore, the glue dot on the other side (i.e. the glue dot closest to the actuator arm assembly) sometimes pulls away due to unpredictable thermal expansion differences between plastic and metal.
For these and other reasons, a good adhesive bond at the glue dot is essential for efficient and cost effective manufacturing. One proposed solution could be to use larger glue dots; however, there are several problems associated with large glue dots. Glue application can be unpredictable: liquid glue tends to "wick" along the wire and to spread to unwanted locations rather than remain in the desired location, causing difficulties in quality control. Uncontrolled spreading increases the probability that a part will be unusable. Furthermore, a larger glue dot is more susceptible to thermal expansion stresses. And, glue wicking could cause the thin wires to be too stiff and adversely affect performance. Additionally, due to requirements for close spacing between disks in modem disk drives, the greater height of such a larger glue dot could cause the thickness of the suspension assembly to cause difficulties during merge of the suspension assemblies into the disk stack.
Another proposed solution to the adhesion problem could be to use a greater number of small dots. However, this approach increases manufacturing costs by increasing the time it takes to manufacture a part, and therefore is not an acceptable solution. It would be an advantage to provide a system for predictably and effectively gluing the wires to a load beam using only a few glue dots.